CFD Online Discussion Forums - strain rate magnitude

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CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)

- Fluent UDF and Scheme Programming (https://www.cfd-online.com/Forums/fluent-udf/)

- - strain rate magnitude (https://www.cfd-online.com/Forums/fluent-udf/90818-strain-rate-magnitude.html)

Kanarya

September 1, 2014 06:45

Hi,
I am using tensors in udf so my question is:
should I initialize the tensors?or there is no need for it?
for example

PHP Code:


		
			
 for(j=0;j<ND_ND;j++)

{

for(i=0;i<ND_ND;i++)

{

  S12[i][j]=0.0;

}

}

and then 

for(j=0;j<ND_ND;j++)

{

for(i=0;i<ND_ND;i++)

{

  S12[i][j]=....calculate;

}

}

is it ok?
thanks in advance!

m zahid

November 19, 2014 10:01

vorticity vs strain rate

hi, anybody know the difference in equation of vorticity and strain rate in CFD fluent. i want to write the UDF of vorticity in 3D.
if anybody know about this, please share this .
thanks

prasa

July 10, 2018 08:12

Hi,
I know this conversation is very old, but the information here is very important.

I would like to know, shear stress for the incomprehensible fluid is given as following equation, by just removing the linear expansion terms?

$s=\sqrt{(u_{z}+w_{x})^{2}+(u_{y}+v_{x})^{2}+(w_{y}+v_{z})^{2}}$

Is it correct ?

arashfluid

July 17, 2018 03:51

Gradient of strain rate

Hi friends,
How can I write gradient of strain rate (∇γ ̇) in udf?
Can anyone help me?
Thanks,

mdmtramper

February 9, 2021 09:07

Hi, thanks for this :) Does anyone has a good reference for the derivation? Thanks!

mcanoenen

September 23, 2021 02:33

Could you please help about this as well. And could you possibly suggest me a tensor book for a beginner?

Quote:

Originally Posted by rembe (Post 401176)

Hi,

I'm not a expert in fluid mechanics. Can you tell me the difference between the strain rate magnitude:

http://www.cfd-online.com/Forums/vbL...66aad1f8-1.gif

and the mean strain rate:

Sij=1/2*(dUi/Dxj+dUj/dxi)

I need th correct formulation in the SMAGORINSKY-model.

Thank you very much
Michael

Regards,

mcanoenen

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